The major goals of the proposed research project for this continuation year include the following: (a) To study the efficacy as to potency and duration of action of the narcotic antagonists naloxone, naltrexone and its sustained preparation (Yolles) in blocking the EGG and behavioral effects of morphine in naive rats prepared with chronic EEG and EMG electrodes, (b) To study the effects of the narcotic antagonists on the phenomenon of relapse by the chronic administration of naloxone by infusion and naltrexone by injection to post-addiction rats and evaluation of the rate of reestablishment of lever pressing activity and morphine self-injection, (c) It is intended to study the effects of these antagonists on the frequency spectra of the EEG and sleep-awake activity of post-addict rats relapsing to morphine, (d) To examine structure-activity relationships of the currently synthesized narcotic antagonists with regard to their blocking effects of the EGG and drug-seeking behavior of post-addict rats. These agents will first be evaluated in naive rats as to the degree and duration of their blockade of morphine-induced EGG slow bursts. Further evaluation of these antagonists will be undertaken in chronic the inter-injection intervals will be further pursued to delineate any EGG changes reflecting drug-seeking behavior.